The present invention relates to a method for incineration of combustible waste that provides heat utilized in the manufacture of cement clinker where cement raw meal is preheated and calcined in a preheater system with a calciner, burned into clinker in a kiln and cooled in a subsequent clinker cooler. More specifically the invention involves the method of using two separate combustion chambers in series for maximizing the firing of alternative waste fuels, and for simultaneously firing a variety of waste fuels in a cement manufacturing process. The invention also relates to an apparatus for carrying out the method.
Examples of combustible waste suitable for firing in the present invention include whole and shredded tires, furniture, carpets, wood refuse, garden waste, kitchen and other household waste, paper sludge, paper, biomass, petcoke, anthracite, sewage sludge, liquid waste, bleaching earth, car parts, plastic, plastic bales and hazardous medical waste.
From EP-1200778, the contents of which are hereby incorporated by reference, is known a method as well as an apparatus for burning waste, i.e. alternative fuels, in a separate compartment in conjunction with a cement manufacturing plant subject to simultaneous supply of hot air coming preferably from the clinker cooler. The compartment is characterized by having a supporting surface for the waste and furthermore during incineration the waste is transported through the compartment to its outlet in a circular path. The compartment is particularly adaptable to incinerating a wide variety of waste as the retention time allotted to a particular waste material may be simply varied by changing the rotation rate of the waste. It is most suitably utilized for incinerating waste materials that require a relatively long material retention time, i.e. from at least about 5 minutes to about an hour or more, such as, for example, automobile tires, large wood waste, such as large pieces of telephone poles, municipal/household waste and automobile fluff.
In practice, this method and apparatus have proven to be particularly suitable for the incineration of larger waste, providing a significant heat contribution which has improved the total operating economics of the plant. However, the compartment characterized above is not necessarily adaptable for combusting different types of waste simultaneously, each of which may require varying amounts of material retention time.
Alternatively, it is known to utilize down draft combustion (also known at times as precalcining) chambers in cement operations to reduce fuel costs by burning alternative fuels. These combustion chambers are known for having utility for incinerating waste materials, such as liquid waste fuels and finely divided waste fuels that need only a relatively short retention time, i.e. from about 1 to about 10 seconds, such as liquid wastes and finely divided coal and petcoke. These combustion chambers, employed upstream from a calciner, pose problems if there is incomplete combustion, which can happen for example if they are used to combust larger sized waste fuels or a single alternative fuel source that has varying sized particles (for instance, shredded tires having widely varying sized particles) in that there will be a fall out of larger unburned particles into the kiln inlet. Such particles when burned at the kiln inlet will promote reduction conditions in the kiln which will negatively affect kiln performance in a cement making operation.
The present invention overcomes such disadvantages inherent in combustion chambers utilized in a cement making operation while providing the practitioner of the invention the option of simultaneously firing a variety of waste fuels or a waste fuel having varying particle sizes.